The present invention relates to fuel injectors and specifically to an apparatus and method of determining check motion through pressure sensing.
As emissions continue to drive engine development, exact control of the fuel injector becomes vital. By controlling how and when fuel is injected, combustion is enhanced and emissions are reduced. Fuel injectors have improved substantially over the years, particularly with the development of the direct controlled check but more control is still necessary. For example, although, the check is now directly controlled, it would be beneficial to have feedback regarding the exact movement of the check.
In U.S. Pat. No. 6,253,736 B1, issued to Crofts et al., a check feedback system is illustrated. Specifically, the ""736 patent requires the use of a piezo actuator in direct contact with a control valve that controls pressure on top of the needle valve. The control valve must be positioned in close proximity to the needle valve so that at the maximum open position the control valve contacts the needle valve which then creates a axial force that is transmitted back to the piezo actuator. The axial force compresses some of the piezo elements, generating a voltage and causing a spike in the voltage curve. By monitoring the voltage curve, the control system can then determine when the needle valve is at a maximum open position. As can be seen, this system has many limitations, including the requirement of a piezo actuator, which may require substantial space within the injector, placement of the control valve close to the needle valve, and only feedback when the control valve actually contacts the needle valve at the maximum open position.
The present invention is directed at overcoming one or more of the above problems.
In one embodiment of the present invention, a fuel injector comprises a lower body, a tip having an outer surface and a inner surface forming a bore, an orifice disposed within the tip and being opened at the inner and outer surfaces and a fuel passage disposed in the tip and in fluid communication with the orifice. The fuel injector also comprises a needle valve disposed within the bore and being movable between first position at which fluid communication between the orifice and fuel passage is blocked and a second position at which fluid communication between the orifice and fuel passages is open. The fuel injector also includes a fuel chamber disposed in the tip and a pressure control cavity disposed in the lower body and being adapted to receive a pressurized fluid. The needle valve has a first surface open to pressure control cavity and the needle valve is fluidly biased toward the first position by pressurized fluid acting on the first surface. The needle valve also has a second surface and is fluidly biased toward a second position by pressurized fluid acting on a second surface. Additionally, the fuel injector includes a sensor disposed in the lower body and being adapted to measure a pressure within the pressure control cavity.
In another embodiment of the present invention, a method of timing a needle valve in a fuel injector composites steps of sensing a pressure in a pressure control cavity, delivering feedback signal in response to a sensing step and adjusting the needle valve timing in response to the feedback signal.